Biconical electromagnetic horn



y 8, 1952 w. L. BARROW 2,602,894

BICONICAL ELECTROMAGNETIC HORN Filed Feb. 19, 1946 OSCILLATOR INVENTOR. WILMER L. BARROW ATTORNEY Patented J My 8, 1952 UNITED STATES PATENT OFF-ICE Wilmer L. Barrow, Manhasset, N. Y.

Application February 19, 1946, Serial No. 648,767

4 Claims.

1 The present invention relates to radio-antenna systems comprising electromagnetic horns, and more particularly biconical horns. The present application is a continuation-in-part of application, Serial No. 155,489, filed July 24, 1937, now Patent No. 2,425,716.

An object of the present invention is to provide a new and improved electromagnetic horn suitable 'for radiating or absorbing at ultra-high frequencies uniformly and substantially in all directions of azimuth in a plane along the surface of a cone, or along other surfaces of revolution.

Other and further objects will be explained hereinafter and will be particularly pointed out in the appended claims.

The invention will now be more fully described in connection with the accompanying drawings, in which Fig. 1 is a diagrammatic view of circuits and apparatus showing, in perspective, an electromagnetic ibiconical horn embodying the present invention, vertically disposed, and connected to suitable sending equipment through the medium of a coaxial line; and Fig. 2 is a similar view of a modified horn connected to a hollow-pipetransmission line.

In Fig. 1, there is shown, for illustrative purposes, a transmission system comprising an ultra-high-frequency-oscillator electromagneticwave translating means 2, provided with a modulator 3, which may be modulated in any desired way, as by means of a microphone 4. The modulated output may be fed to a radio-frequency amplifier 6 that maybe coupled to a circuit 8 having two-wire output-conductor connecting.

leads l9 and I2. One of the leads, as the lead I0, is shown connected to the lower end of the outer tubular or cylindrical conducting body portion 35 of a coaxial-line system. The tubular member 35 thus serves as a conductor to which some of the electric lines of force are attached. The other lead, as the lead "I 2, is shown connected to thelower end of the inner conducting exciting or absorbing stem or rod M of the coaxial-line system, disposed approximately axially of the tubular body portion 35. The leads I and I2 may, however, be connected to other types of terminal device, including conventional parallelline or other systems and, in particular, to an elongated vertically disposed tubular-conductor hollow-pipe uniconductor wave-guide transmis-.

sion system 21, shownin Fig. 2 as electrically open at its upper end and of circular cross-section. The wave-guide 21 may enclose airjor any other suitable dielectric medium, and its transverse dimension is substantially equal to or 2 slightly greater than the critical dimension for the lowest-order electromagnetic waves that will pass through the hollow pipe 21.

The upper end of the outer tubular body por-' tion 35 of the coaxial-line system of Fig. l, and of the hollow-pipe guide 21 of Fig. 2, is shown, at 25 and 23, respectively, smoothly, roundly and continuously flaring externally back on" itself, with a slight curve, to fiaregradually outward into a lower conductive horn-member expanse 29. The upper extremities of the slightly flaring portion of the tubular body portion 35 and of the hollow-pipe guide thus carry the lower "horn member 29 to couple the hornmember 29 to the upper axial end of the tubular. member. 35 of Fig. 1 and the electromagnetic wave-guiding passage defined by the wave-:guide 21 of Fig. 2, respectively. j v

The conductive expanse 29, moreover, becomes thus provided withan opening orap'erture therein near its inner axial end, where it is joined to the upper extremity of the slightly flaring portion 23 or 25. Thewave-guide 21 opens into the said passage near the said inner end thereof for the transmission of the waves through the in terior thereof. The translatin means ,2 is removed from the said open end, as itis connected by the conductors l9 and I2 at the lower end of the coaxial line 35, respectively.

The upper end of the inner rodjl l of the [co axial line 35, I4 is joined to an upper conductive horn-member expanse 3|; shown flaring continuously vertically outward from its'junction with the member M to constitute, with the horn member 29, an outwardly directed biconical horn defining a flaring radial transmission line. ,'In or near the central interior or throat regionof the biconical horn, where the corresponding horn-like member 3| of Fig. 1 is joined tojthe rod It, the upper horn member 3| ofFig. 2 is shown provided with anapex 33 which may, if

, desired, be pointed. The small'apic'al end 33 of the member 3| is shown extending down into the.

35, It, respectively, at the center of the biconical horn, and'inverted with respectto each other, upward and downward, respectively, The common axis of the horn members 29 and 3| and of the coaxial line 35, I4, as well as of the wave-.

guide 2'! alon which the horn members 29 and 3| are spaced vertically in substantially vertical l4 and the wave-guide 21,

3 alinement with each other, may [be defined as the principal axis 01' line of reference of the biconical horn.

A radio-broadcast antenna system is thus provided, comprising a biconical horn defining a pair of conductive expanses 29 and 3| spaced apart in axial alinementbutjuxtaposed and shaped to form between them a wave-guiding transmission line mounted at the open upper end of the wave-guide 21 or at the upper-end of the coaxial line 35, M. The biconical wave-guiding transmission line guides the waves between the said open upper end and the outer peripheral extremity of the transmission line. The transmission line comprises an annular wave-guiding passage or space, in the form of a solid of revolution, of rather small or minimum thickness ,atthesaid lineof reference, but expanding on all sides therefrom to flare progressively outward, in all azimuthal planes, into a large peripheral portion at the exterior orouter end region of the horn that is electrically open to free space, .in order to permit the horn to receive ,ultra-high-frequency electromagnetic wavesfrom-space-or to transmit electromagnetic wavesoutinto space. The upper ends of the wave-guide21 andof the coaxial line 35, a are correspondingly open for the radiation or re.- ception of the wave through the biconical-horn wave-guiding .annularspace or passage. The biconical horn 29, 3| is thus excited centrally, at its interior or-throat, by ,means, respectively, of the coaxial line .35, 1.4, and .the wave-guide 21, the interior of which is disposed in communicating relation .with this annular wave-guiding passage, and it similarly absorbs waves from space centrally, .at its interior.

The horn members .29 and 3| may be constituted of formed sheet of conducting material, like meta1,.such as copper or aluminum, or they may be constituted of other material if their inner or oppositely disposed walls are otherwise rendered conductors of the waves. The same applies to the tubular portion .35 of Fig. 1 and the hollow-pipeguide 21 015 Fig. 2. If constituted of metal of other conducting material, the wave guide 21 willshield the waves therein.

The surfaces of revolution of the horn :members 28 and 3| may be constituted of frusto-conical flanges. They are preferably not truly conical, however, but approximately or substantially so, being shown curved somewhat away from the true cone shape in order that the annular biconical-horn wave-guiding space between them may flaringly expand more rapidly than linearly. The horn members 23 and 3| are thus enabled to ,cooperate better for the purpose of enhancing the horizontal directivity of the biconical-horn radiation and increasing the frequency response. Whether or not strictly conical, however, the biconical horn is circularly symmetrical about its principal axis.

The flaring upper ends 23 and 25 of the waveguide 21 and the tubular portion 35 of the coaxial line 35, M, respectively, function not only as wave-guide feeders, but also as vertically disposed horns. They are shown flaring but slightly, in order that the lengths of the horns 23 and 25 thereby provided may be at least several times the wave-length of the waves radiated or received by the biconical horn. The biconical-horn structure is shown arranged as a horizontally directed continuation of the vertically disposed portion 23 or 25. The gradual expansion of the electromagnetic. field com ising the guided waves i iated. b t e horns 23 a d 25, therefore, becom s increased by the biconical horn. The conductive surfaces 29 and 3| will modify the radiation pattern of the wave-guide 21 or the coaxial line 35, H3, by impeding radiation of the wave launched or otherwise introduced into the wave-guide 21 for transmission to the said upper open end, or transmitted to the biconical horn by the coaxial system, 35, M, thereby enhancing their radiation in the horizontal direction. For a given degree of electromagnetic-field expansion, therefore, a smaller biconical horn structure 29, 3| is required than would have been the case in the absence of the horn-like feeder 23 or 25.

The horn members 29 and 3| are shown lying substantially wholly on opposite sides of a horizontal planelthrough the center of the biconical .horn, substantially at right angles to its principal axis, at the upper end of the wave-guide 21 or the coaxial line 25, I4. The directivity pattern will therefore be such that the main portion of the radiant energy will be concentrated in that horizontal plane. .Depending upon theshapes of the ,horn members .29 and 3 I, however, the waves may .beradiated out-at any convenient angle to the horizontal.

' Sending or receiving apparatus may be connected to the two-wire connecting leads l0 and I2.

As before stated, Fig. '1 illustrates a sending system. The corresponding connections for receiving radio waves intercepted by the said annular passage of the biconical horn at the exterior periphery thereof, from .free space, will be understood by persons skilled in the art without further illustration. The coaxial line 35, I4 or the wave-guide 21, as the case may be, is connected to sending translating apparatus 2 for exciting the biconical-wave guide transmission line, or with receiving translating apparatus (not shown) for receivingradio waves intercepted from space. The connection is shown as effected by means of the two-wire connecting leads l0 and 2, either through the coaxial line 35, M or through the tubular-conductor hollow-pipe. wave-guide 21. The biconical horn 29, 31 is thus excited centrally, at its interior or throat, by means, respectively, of the coaxial line 35, I4, and the wave-guide 21, the interior of which is disposed in communicating relation with the annular wave-guiding passage, and it similarly absorbs waves from space centrally, at its interior. In both sending and receiving, the sending translating means 2 or the corresponding receiving translation means (not shown) is coupled through the opening or aperture at the upper end of the coaxial line 35, I4 or the wave-guide 21, in radio-wave-energy transfer relation, at the central end of the biconicalhorn transmission line, to the radial transmission line provided by the biconical wave-guiding passage between the horn members 29 and 3|, for transferring energy from or to the biconical horn.

In transmission, in the system of Fig. 1, modulated ultra-high-frequency electromagnetic energy may be taken by the conductors H) and I2 from the sending translating apparatus 2 and delivered to the concentric line 35, I4, by which it will be transmitted to the said interior or throat of the horn. In the system of Fig. 2, dielectrically guided electromagnetic waves may be conducted by the conductors HI and I2 to the lower end of the wave-guide 21, so as to be launched or transmitted upward along the wave-guide 21. The modulated electromagnetic energy will then be propagated radially. outward through the said annular wave-guiding space or passage of the biconical transmission line to the said large exterior peripheral portion of the biconical-hormfl Upon arrival at this peripheral portionjof thebiconical horn, the electromagnetic waves become readily disattached from the horn, continuing thereafter to travel beyond this peripheral portion, for radiation forward out 'into' freespace', as ordinary modulated radio waves. The waves will be radiated outward into space substantially uniformly in all directions of azimuth along the periphery of this transmission line. The biconical horn 29, 3| thus constitutes a directive electromagnetic radiator.

Similar but reverse operation will take place during reception of such waves. 'The modulated electromagnetic waves will be received at the large periphery of the biconical horn 29, 3| and, after traveling through the flared biconicalehorn annular space, will be absorbed by the coaxial line [4, 35 or the wave-guidel'hf and will be communicated to the conductors Ill and I 2, by which they will be conducted to a receiving system (not shown), where the signals comprising the intelligence will be demodulated.

The biconical horn may thus be connected to sending or receiving apparatus, at its throat in terior, and to free space, at its periphery. for purposes of either radiating radio waves into, or absorbing them from, space. If the biconical horn is used for the transmission or the reception of ultra-high-frequency waves of wavelengths below ten meters, its dimensions may be kept reasonably small.

The horn members 29 and 31 of the biconical horn are provided with flaring guiding surfaces or guiding walls, of progressively greater cross-sectional area from the interior of the biconical horn toward its periphery, that connect the interior of the horn with its periphery. The biconical horn thus operates to guide the electromagnetic waves traveling through the dielectric within it tangenially along the said conducting guiding surfaces in all directions of azimuth smoothly, continuously, and without interruption. In reception, the electromagnetic waves received from space at the periphery of the biconical horn are thus guided by the said surfaces to its throat interior. In transmission, the electromagnetic waves generated at the interior of the horn are guided along the said surfaces to the periphery thereof, for propagation forward out into space. The waves become thus slidingly attached to the guiding surfaces and they remain so continuously attached throughout their sliding guided movement along this horn surface, from the throat interior of the biconical horn until they reach the exterior periphery thereof. A similar operation takes place during reception.

The higher-order waves travel through the di electric of the wave-guiding biconical-horn passage with a phase velocity difierent from that of light. Near the throat of the horn, the phase velocity may be very much greater than the velocity of light. The phase velocity decreases as the periphery of the biconical horn is reached, until just at or beyond the periphery, the phase velocity may be exactly the same as that of light.

The distance between the base edges 39 and 4| of the horn members 29 and 3| may be several wave-lengths. The radial length of the biconical transmission line, or the distance between the junction of the horn member 3| to the rod I 4 of Fig. 1, or between the apex 33 of the horn member 3| of Fig. 2, at the axial end at the throat of the horn, to its exterior peripheral end, may be varied over wide limits, from a preferably small value,

6. atleast a. wave-length; up'td substantially greater than a wave-length or'moreflofthe waves guided by the biconical-horn transmission system Par ticular distances, however.are peculiarly adapted to the excitation of waves of particular'f types in the horn; for different type's'of horn waves, and combinations of the same, may b'es'eparately excited and propagated within the horn for transmission, or absorbed by the horn} for reception. Higherorder types of wavesare discussed by S. A. Schelkunoff in two articles, entitled; Transmission-Theory of spherical' wave's'flBell System Monograph 3-1092; '1939,'=""an'd Transmi sion Theory of Plane Electromagnetic-Waves, Proceedings of the'Institute' ofRadio Engineers, vol. 25, pp. 14571492, November, 1937.

Lower-order symmetric vertically polarized transverse electromagnetic or TEM horn waves may be-excited or received at ornear'the center of throat of the biconical horn. The ma netic and electrostatic lines of the wave are both transverse to the direction of propaga tion. ThelI'EM is the' sim'plest type of wave wherein the magnetic'lines form'concentric circles aboutthe principal axis dfthebiconical horn 19, 3 I, and] 'wh'eren'qj 'the electrostatic lines extend in arcs between the horn'membe'rs 2 9 and 3!.

Other waves sometimes used in biconical horns are of transverse magnetic or TM type. These waves have their electric lines in the form of partial loops extending; radially from the walls of the guides toward. the center, then longitudinally along the horn and then back to the wall from which they started, and. may have additional closed loops in the space between the two surfaces in higher orders. The magnetic lines are circles concentric with the axis of the tube and linking through the partial loops of the electric lines so that these magnetic linesare wholly transverse to the direction of propagation. Examples are TMo,1 and TMo,z waves.

The electrostatic lines of the lower-order horizontally polarized transverse electric or TEo,1 wave, like those of the TEM wave, are wholly transverse to the direction of propagation. They form concentric circles about the principal axis of the biconical horn 29, 31. The corresponding magnetic lines, however, are

partly transverse and partly longitudinal. Theyv form loops linking about the electrostatic lines,

and lying wholly in radial planes passing through.

- the principal axis of the biconical horn.

' at the operating radio frequency and the angle of flare being acute, and electromagnetic wave translating means at the central end of said line for exciting said line or for receiving radio wave power intercepted thereby.

2. A radio-antenna system comprisinga pair of continuously curved conductive expanses juxtaposed and shaped to form between them a eves idine assese hat flaresna w d fr m an irmer; re i n o; an. .11 2 5 re ion hat s. pe o r e space tor the radiation rec n iq f io. w es, the pas age hav newB th-g am an on wavelen h and ufi ient to ta on wave. ide pro eresd; a e ui e x t e or receiving means coupled to the passage atthe inner region, 7

A ra ion e na sys em q m r i sap ir of urved. conductive expanse juxtaposed and a e Q orm be weentn m a u d p a e tha ime tw ml an n len to a ou re ion th is pen o free spac for the radiatign orreception of radio waves, the p e hav n a en th rea an he wave-length of the waves-, one of the conductive expanses having an opening at the inner region of the. passagaand wave, guide means coupled through the opening inwave-energy-transferelation with'the passage. I

4. A direotiye radiating system comprising two extended wave guidingmembers at least one wavelength 8 disposed adjacent each other and shaped so that at least their proximate surfaces have substantially the form of curved sur-, a es o reve at on ou a c mmon x at least one. of; said suriaces being sufllciently convex so directi vely.

V I WILMER L. BARROW.

REFERENCES CITED The following references are of record in the file of-this patent:

U ED S TE PA TS Number Name Date 2,175,252 Carter Oct. 10, 1939 2,206,923 Southworth July 9, 1940 2,231,602 Southworth Feb. 11, 1941 2,235,506 'Schel kunofi; Mar. 18, 1941 2,283,935 King May 26, 1942- 2,369,808 Southworth T Feb. 20,1945

' FOREIGN PATENTS Number Country Date 493,695 Great rema n Oct. 13, 1 93s 

